add_action('load-page-new.php','custom_help_page');
add_action('load-page.php','custom_help_page');
function custom_help_page() {
  add_filter('contextual_help','custom_page_help');
}
function custom_page_help($help) {
  // echo $help; // Uncomment if you just want to append your custom Help text to the default Help text
  echo "<h5>Custom Help text</h5>";
  echo "<p> HTML goes here.</p>";
}

http://sixrevisions.com/wordpress/10-techniques-for-customizing-the-wordpress-admin-panel/

If you take a look at the top right of the WordPress Admin panels you’ll see a button that says "Help." When you click it, Help text slides down.

Edit the Help Dropdown Text

wordpress, help

PHP